Present invention is related to fiber-optical transmission devices, and more particularly to a clip structure for fixing an optical fiber with respect to an optical source such as a laser diode.
In many modem communication networks, signals are transmitted in optical form through fibers for communication. Furthermore, optical fibers are the preferred medium to transport light from a source to the location of interaction with matter, e.g. fiber optical amplifiers, laser welders, etc. Important parts of these networks and devices are the arrangements where an optical signal, generated in a laser light source, is coupled into the transmission fiber. Optical coupling arrangements therefore have received much attention, because the energy lost in the coupling process should be minimal. Furthermore, the fabrication of such devices which have very small dimensions and tolerances is a complicated and delicate task.
In these devices, the fiber tip must be held very tightly in place with respect to the optical source. On the other hand, they must still leave the possibility to fine tune the fiber position during mounting in order to achieve maximum transfer of the optical energy into the fiber.
Several devices and methods were suggested and are used for adjusting and fixing the fiber in optical transfer modules. Many of them provide a holding member for the fiber, which is fixed to a ground plate, and to which a tube or sleeve enclosing the fiber end is fixed by spot welding using lasers as energy source.
In U.S. Pat. No. 4,837,768 issued to P. Schmid a laser module and a method for coupling an optical fiber thereto are disclosed. A mounting block is provided which has an opening (a bore) for a fiber end sleeve. Separate holders are placed over the sleeve at the front and rear ends of the mounting block, and in sequential adjustment steps the holders are fixed to the mounting block and then to the fiber sleeve by soldering or laser welding. Disadvantages of this method and arrangement are the facts that the fiber sleeve must be introduced into the mounting block (bore), and that several separate parts, i.e. the holders and the mounting block, must be attached and kept in place during fixing.
A method of optically coupling optical fibers to injection lasers is described in U.S. Pat. No. 5,570,444 to Janssen and Donaldson. A slotted rod is provided for holding the fiber with a special fillet of solder. This slotted rod in turn is fixed by welding spots to slide members close to its front end and to a saddle part at its back end. All these parts, in particular the slide members, must be accuately positioned and held in place and separately fixed during the alignment (adjustment) process which is difficult and time consuming because of the various separate entities involved.
Another approach is disclosed in U.S. Pat. No. 5,619,609 to Pan et al. entitled xe2x80x9cFiberoptic Support Clipxe2x80x9d. The clip constitutes a channel into which the fiber sleeve is inserted from above and then, after optical adjustment, fixed by laser welding to the top edges of the walls of the channel. It appears that after initial placement of the fiber sleeve on the fiber, the sleeve must be removed and then inserted again for proper fiber adjustment and clip placement. This increases cycle time during manufacturing. Furthermore, fine adjustment after clip placement might be difficult because of the so-called slip friction.
Generally the known fiber fixing devices and methods have stringent tolerance requirements on high precision parts, or require pre-weld forming, or selection of mating parts for tight fit. All these facts are inherently increasing production time and manufacturing costs.
It is an object of the invention to devise a fiber holding device which consists essentially of a single structure. A further object is to provide a fiber holding device which does not necessarily require small tolerances but still allows precise adjustment and fixing of the optical fiber in relatively few steps.
The invention for achieving this object, as defined in the claims, is a fiber holding clip for fixing an optical fiber secured in a fiber support tube, with respect to a light source, having a rigid front part and a flexible back part, so that for adjusting the position of the fiber tip, the flexible back part can be deformed to move the fiber with the fiber support tube while in the rigid front part a pivot point is available; a further aspect of the invention is an optical module subassembly for holding an optical fiber secured in a fiber support tube, with respect to a light source, the subassembly comprising a clip consisting of two fiber holding partsxe2x80x94a rigid front part and a flexible back part xe2x80x94on common base flanges, wherein welding spots fixing the base flanges to a mounting plate are specifically arranged to increase stability at the rigid front part and to increase flexibility at the flexible back part of the clip.
This allows, in particular, fast part handling as well as easy adjustment and fixing of the optical fiber in an optical coupling module, in a completely automated process. The resulting optical fiber holding assembly is mechanically stable.
With the invention, it is also possible to use the known method of laser hammering for fine adjustment of the fiber after placement (aligning) and initial fixing.
Use of the inventive fiber clip results in very precise and stable alignment between fiber tip and laser light source. No parts matching and multiple part are necessary. Therefore the invention allows module packaging with high yield and high reliability, enables high throughput of the assembly station, and results in a decrease of manufacturing cost. No removal or displacement of the fiber after alignment is necessary for clip loading. The structure allows two methods for fine alignment: Laser hammering and re-bending. The bending mainly takes place in the clip and not in the fiber support tube which otherwise could lead to reliability problems in the solder zone of the support tube.